Conventional power actuated industrial clamps typically employ air or hydraulic linear pistons to actuate clamp arms through toggle linkage, a recent version of which is disclosed in U.S. Pat. No. 4,458,889 issued on July 10, 1984. Such clamps, as used in industrial production for repetitively holding identical work pieces during processing operations, are generally limited to a single dedicated clamping position with toggle linkage near or preferably at centered position, at which the clamp will remain locked upon release of actuating pressure and at which maximum clamping force may be exerted for a given actuating pressure. Any clamp setting appreciably short of centered toggle linkage necessitates retention of actuating pressure for the duration of clamping requirement.
In order to provide alternative electrically powered clamps, various electric motor drives have been adapted to provide clamping action, as in actuating a work clamp through worm gearing, such as disclosed in U.S. Pat. No. 2,395,242 or in actuating a tubular piston through a lead screw driven by an offset electric motor such as disclosed in U.S. Pat. No. 4,137,784.
Without application to the clamping art, certain electric motor actuated jacks or other screw actuated devices are disclosed in U.S. Pat. Nos. 733,614, 1,279,346, 1,404,862, 1,543,181, and 2,956,188, each of which has the common feature of a feed screw extending through and in axial alignment with the electric motor.
In the last of such patents, employed for valve operation, a control indicator rod extends from the tail end of the feed screw out of the motor housing in a manner having some similarity to a control feature employed in the present invention.
With regard to requirements of industrial clamps, it is a generally recognized desirable feature for the clamp to be self-locking in its clamping position to avoid the requirement for maintaining power-on actuation.